Finite-size effects in the dynamics of neutrally buoyant particles in turbulent flow

TL;DR

This study investigates how finite-size neutrally buoyant particles behave in turbulent flows, comparing numerical simulations with analytical models to understand the effects of particle size on their dynamics.

Contribution

It adapts a spectral method to study finite-size effects, revealing the dominance of Faxen corrections for small particles and inertial-range physics for larger particles.

Findings

Faxen corrections dominate for particles up to four times the Kolmogorov scale.

Particle dynamics for larger sizes align with inertial-range physics predictions.

The method provides insights into the validity limits of point-particle models.

Abstract

The dynamics of neutrally buoyant particles transported by a turbulent flow is investigated for spherical particles with radii of the order of the Kolmogorov dissipative scale or larger. The pseudo-penalisation spectral method that has been proposed by Pasquetti et al. (2008) is adapted to integrate numerically the simultaneous dynamics of the particle and of the fluid. Such a method gives a unique handle on the limit of validity of point-particle approximations, which are generally used in applicative situations. Analytical predictions based on such models are compared to result of very well resolved direct numerical simulations. Evidence is obtained that Faxen corrections give dominant finite-size corrections to velocity and acceleration fluctuations for particle diameters up to four times the Kolmogorov scale. The dynamics of particles with larger diameters is dominated by inertial-range physics, and is consistent with predictions obtained from dimensional analysis.